Embryonic Development: Gastrulation and Organogenesis

3-4 Weeks: Gastrulation

• The embryo undergoes gastrulation, where the blastula transforms into a gastrula
• Three primary germ layers form:
  1. Ectoderm: gives rise to skin, nervous system, and sensory organs
  2. Mesoderm: forms muscles, bones, and internal organs
  3. Endoderm: develops into lining of digestive system and respiratory tract
• Gastrulation occurs through a process of invagination, where cells move inward to form a double-layered embryo

4-5 Weeks: Organogenesis

• The three germ layers begin to differentiate and organize into specific tissues and organs
• Neural tube formation:
  • Ectoderm invaginates to form a neural groove
  • Neural groove folds in to form a neural tube, which will develop into the brain and spinal cord
• Heart formation:
  • Mesoderm differentiates into cardiac tissue
  • Heart tube forms and begins to divide into four chambers
• Somite formation:
  • Mesoderm segments into repeating blocks called somites
  • Somites will develop into muscles, bones, and skin of the back

5-6 Weeks: Limb Development

• Limb buds form as swellings of mesoderm on either side of the body
• Upper limb buds develop into arms, forearms, and hands
• Lower limb buds develop into legs, shins, and feet
• Digits form as mesoderm condenses into finger and toe rays

6-8 Weeks: Organ Maturation

• Eye development:
  • Optic vesicles form from ectoderm
  • Lens and retina develop from optic vesicles
• Ear development:
  • Otic placodes form from ectoderm
  • Inner ear structures develop from otic placodes
• Brain development:
  • Neural tube differentiates into forebrain, midbrain, and hindbrain
  • Brain structures begin to take shape, including cerebrum, cerebellum, and brainstem

Embryonic Development

• During gastrulation, the blastula transforms into a gastrula, forming three primary germ layers: ectoderm, mesoderm, and endoderm.
• Ectoderm gives rise to skin, nervous system, and sensory organs.
• Mesoderm forms muscles, bones, and internal organs.
• Endoderm develops into the lining of the digestive system and respiratory tract.
• Gastrulation occurs through invagination, where cells move inward to form a double-layered embryo.

Organ Formation

• During organogenesis, the three germ layers differentiate and organize into specific tissues and organs.
• Neural tube formation: ectoderm invaginates to form a neural groove, which folds in to form a neural tube, developing into the brain and spinal cord.
• Heart formation: mesoderm differentiates into cardiac tissue, forming a heart tube that divides into four chambers.
• Somite formation: mesoderm segments into repeating blocks called somites, developing into muscles, bones, and skin of the back.

Limb Development

• Limb buds form as swellings of mesoderm on either side of the body.
• Upper limb buds develop into arms, forearms, and hands.
• Lower limb buds develop into legs, shins, and feet.
• Digits form as mesoderm condenses into finger and toe rays.

Organ Maturation

• Eye development: optic vesicles form from ectoderm, developing into the lens and retina.
• Ear development: otic placodes form from ectoderm, developing into inner ear structures.
• Brain development: the neural tube differentiates into forebrain, midbrain, and hindbrain, with brain structures taking shape, including the cerebrum, cerebellum, and brainstem.